OLR Research Report

April 8, 2008




By: Paul Frisman, Principal Analyst

You asked about the extent of Connecticut's problem with invasive species of milfoil and what the state is doing to address it.


Three invasive milfoil species have been found in Connecticut. The most common are Eurasian milfoil and variable-leaf milfoil. These plants were first found in Connecticut several decades ago, and have now spread to dozens of lakes and ponds, where their dense mat-like growths can harm lakes and aquatic life. Boaters may inadvertently help spread these weeds by carrying fragments from one lake or pond to another on their boats and trailers.

In 2003, the legislature banned the sale, purchase, cultivation, distribution, and transplantation of seven invasive plants, including Eurasian and variable-leaf milfoil. It created a state Invasive Plants Council to recommend ways to control and stop the spread of invasive species, educate the public about them, and publish and update a list of invasive and potentially invasive plants. In 2004, the legislature added 74 plants to the state invasive plant list, including parrot-feather, a third species of invasive milfoil.

In 2007, the legislature appropriated $500,000 in FY 08 and FY 09 to the Department of Environmental Protection (DEP) to control invasive species. DEP must use the money, in part, to hire an invasive plant coordinator to oversee both terrestrial and aquatic invasive plants. DEP is seeking to use some of this funding, plus some federal funds, to hire an aquatic nuisance species coordinator to coordinate programs affecting invasive aquatic plant and animal species.

DEP also provides technical assistance to people concerned about invasive plant problems. The Connecticut Agricultural Experiment Station (CAES) also provides technical assistance, and conducts surveys, research, and workshops on aquatic invasive plants and their control.

The legislature this year has before it legislation that would, among other things, bar municipalities, between July 1, 2008 and October 1, 2013, from adopting ordinances regulating the retail sale or purchase of invasive plants.


Eurasian milfoil (Myriophyllum spicatum), variable-leaf milfoil (Myriophyllum heterophyllum), and parrot-feather (Myriophyllum aquaticum) are three invasive milfoil species that are present in Connecticut.

Eurasian Water-Milfoil

According to “A Guide to Invasive Aquatic Plants of Connecticut,” published in 2005 by CAES, Eurasian milfoil occurs in more than 40 ponds and lakes in Connecticut, primarily in the western part of the state, as well as in many areas of the Connecticut River.

Native to Europe and Asia, Eurasian milfoil was first reported in this country about 60 years ago. Once established, Eurasian milfoil spreads aggressively and is difficult and costly to manage. It can grow into new plants from fragments carried from lake to lake on boats and boat trailers.

According to CAES, Eurasian milfoil, first found in Connecticut in 1979, is regarded as one of the most serious invasive plant threats in the U.S. It forms dense leaf canopies that can shade out native vegetation, alter water quality, decrease water oxygen levels, increase water temperature, and interfere with boating and other forms of recreation.

Variable-Leaf Milfoil

Variable leaf milfoil is native to the southern U.S. It first arrived in Connecticut in 1936, and, CAES reports, has become a nuisance in many Connecticut lakes, especially in the southeast part of the state. It is known to occur in at least 30 ponds and lakes in the state, and appears to prefer water with lower pH and alkalinity than Eurasian milfoil. Like Eurasian milfoil, variable leaf milfoil produces long stems that rise to the water's surface, where they spread, producing dense mats of vegetation. Control of this species can be difficult, and CAES scientists are researching the effectiveness of spot herbicide treatments.


Parrot-feather is an ornamental milfoil species native to the Amazon. It is commonly sold for use in aquariums and water gardens. Unlike the other two milfoil species, its leaves rise above the water surface, making it relatively easy to recognize. According to CAES, parrot-feather has been collected in few Connecticut locations, but the species overwinters here and may represent a serious threat.

Milfoil Control

According to “Nuisance Aquatic Vegetation Management,” a guidebook published by DEP (attached), people should not cut milfoil to control it, since each piece can grow into another plant. The guidebook states that the most effective chemical controls are systemic herbicides applied at low dosages. But anyone seeking to use a chemical to control an aquatic plant must obtain a DEP permit (CGS 22a-66z).


In 2003, the legislature approved PA 03-136, which:

1. named seven invasive plants, including Eurasian and variable-leaf milfoil;

2. made it illegal to import, move, sell, buy, transplant, cultivate or distribute them; and

3. created a nine-member Invasive Plants Council.

Among other duties, the council must recommend ways to control and abate invasive plants, and annually publish and update a list of plants considered invasive or potentially invasive (CGS 22a-381 through 22a- 381d). The act also required DEP-approved safe boating courses to teach boaters how to properly inspect their boats and trailers for vegetation, and safely remove it (CGS 15-140e (f)).

In 2004, the legislature enacted PA 04-203, modifying some of the invasive plant laws, and adding 74 additional plants, including parrot-feather, to the invasive plant list.

In 2007, the legislature appropriated $500,000 for FY 08 and FY 09 to DEP to control invasive species. The DEP commissioner must use this money to:

1. hire an invasive species coordinator,

2. develop an early detection and rapid response policy,

3. educate the public about invasive species,

4. fund Agriculture Department and CAES inspectors, and

5. provide grants to municipalities to control invasive species on publicly accessible land and waters (PA 07-4, June Special Session 8).

DEP also is seeking to use some of this funding, together with funding from the U.S. Fish & Wildlife Service, to hire an aquatic nuisance species coordinator to coordinate programs affecting invasive aquatic plant and animal species.

In 2008, the legislature is considering a bill (HB 5147) that would, among other things, prohibit, from July 1, 2008 to October 1, 2013, municipalities from adopting ordinances regulating the retail sale or purchase of invasive plants. It allows such plants to be moved for specific purposes and makes other changes to invasive plant laws. The Environment Committee voted HB 5147 out of committee on February 27, 2008.

We have attached the relevant public act summaries and bill analysis for HB 5147.


More information on the Connecticut Invasive Plants council is available at:

More information on invasive plants from CAES can be found at:|

DEP information on invasive plants can be found at: and at: DEP: Lake Water Quality Management Program.

The state's Aquatic Nuisance Species Management Plan can be found at:

The link to the National Invasive Species Information Center is: